WE use a base.css file for all our targets, and for our mobi targets an additional mobi.css file is used to override some of the base css settings and add additional css settings that the kindle needs to format the text correctly.

KindleGen raises this warning if you're using the position property outside of a fixed-layout book. However, it does appear to function properly in the currently available readers: Kindle Fire, Kindle for Android, Kindle for PC, and Kindle Previewer.